Carlos Jaschek

Early type stars with abnormal spectra

Abstract One of the areas which have received a great deal of attention in recent years is the field of the so-called early type peculiar stars. It seems that a review paper on the subject could be of some use, since it helps to visualize both the problems which have been solved and those which have not been solved or studied yet. The present review will not deal, however, with the whole field, but only with one aspect of it, namely the purely spectroscopic side. No attempt is made to cover theoretical aspects, nor explanations of the phenomena observed, since these have been covered in some excellent review papers dealing with either Ap or Am stars or both. The review will deal thus primarily with what one could call “visual spectroscopy”. We hope to demonstrate in the following pages that there is still much room and also much need for this technique. This is due mainly to two facts: first that no two peculiar stars are identical and second that at least some members of the group are spectrum variables. Much confusion has been produced in this field by sweeping generalizations about the behaviour of “all” peculiar stars of a given type, made on the basis of one or two stars analysed in detail. The basic question which is almost never asked is how representative these examples are of the whole group. This is, among others, a task of “visual spectroscopy”, to select typical representatives from the study of large samples. Only then can individual stars be studied profitably and the results generalized for the whole group which they represent. Our subject will be subdivided into four parts. The first will deal with Ap stars, the second with Am stars and the third with Bp stars. This arrangement permits us to deal first with the stars for which we know most and proceed then to less-known stars. The fourth and last part will deal with the conclusions.

THE FREQUENCY OF SPECTROSCOPIC BINARIES

differed by more than 20 km/sec. The results gave 20 percent for all main-sequence stars and somewhat less for giants and supergiants. Petrie (1960) discussed the percentage of the spectroscopic binaries from another point of view and reached different conclusions. He considered three groups, of about 500 stars each, of B, A, and F5-M objects for which at least three individual radial velocities existed. He established then the observed dispersion of the individual velocities and subtracted from this the distribution of

HD 49798, A NEW O-TYPE SUBDWARF

The present paper reports the discovery of a new O-type subdwarf, HD 49798.1 We give here a short description of this interesting object, which deserves more detailed study. This star was observed by the writers as part of a regular program of early type stars which is being carried out at the Bosque Alegre station of the Cordoba Observatory. Five plates of this object (listed in Table I) were taken with the grating spectrograph at a dispersion of 42Â/mm. The wavelength region of our plates runs from A 3200 to A 4900. Visual inspection of the plates discloses a very unusual spectrum corresponding approximately to spectral class O6 whose outstanding characteristics are the strength of ionized helium, the weakness of hydrogen, and the absence of ionized carbon and oxygen lines. The strongest lines in the ultraviolet, besides those of He n are the components of the N iv triplet A 3478-82-84.

Ζ1 SCORPII: A VARIABLE SPECTRUM SUPERGIANT

Very conspicuous and unexpected variations in ffie strength of lines belonging to different elements are reported on ffie basis of 42 A mm-1 spectrograms taken between 1965 and 1970. The variations involve principally He I, N n, and 011. The observations suggest a very turbulent state of ffie outer layers of this star which is probably connected with mass loss from the surface. Key words: stellar spectroscopy - supergiant star - spectrum variable

THE SPECTRUM OF HD 125823

The B-type star HD 125823* was noticed by Miss Cannon (1901) as having a peculiar spectrum; Bidelman ( 1965 ) discovered that its helium lines varied in strength. Plates of HD 125823 were taken during the current spectral classification program in progress at the Cordoba Observatory with the grating spectrograph giving a dispersion of 42 A/mm. One spectrogram of the star, taken at JD 2438844, shows a peculiar spectrum, which can be summarized as follows: